Kishio Hidaka

Concentration profiles and the rafting mechanism of Ni base superalloys in the initial stage of high temperature creep tests

The rafting mechanism is one of the most important and interesting phenomena which appears in Ni base superalloys during high temperature creep tests. The precipitated {gamma}{prime} particles, which are arrayed periodically in the {gamma} matrix, coalesce and form rafting structures in the direction perpendicular to tensile stresses. To understand this phenomenon, element profiles and diffusion process have been investigated in the vicinity of the {gamma}/{gamma}{prime} interfaces. In this paper, the authors analyzed accurate element profiles, especially Al and Cr which are main alloying elements, in the most vicinity of {gamma}/{gamma}{prime} interface regions. The rafting mechanism is correlated with the diffusion process on the basis of Al concentration profiles in a few nano meter distance from the {gamma}/{gamma}{prime} interfaces.

Elastic stress in single crystal Ni-base superalloys and the driving force for their microstructural evolution under high temperature creep conditions

Abstract A mechanism for “rafting” in Ni-base superalloys under high temperature creep conditions is discussed in terms of elastic strain energy. The elastic deformation is analysed by the finite element method and approximate analytical expressions are also deduced for it. The difference between the elastic strain energies at γ channels parallel and perpendicular to the stress axis is derived in closed form, which is used to evaluate the local equilibrium concentration of component elements. The rate of rafting estimated with a simple diffusion model and the concentration distribution data obtained in the present theory agree well with the magnitude of the measured growth rate.

Quantitative study of the plastic slip deformation and formation of internal stresses in Ni-base superalloys

Abstract When nickel-base superalloys deform by creep in a high temperature atmosphere, cuboidal shaped strengthening precipitates of γ′ phase usually grow in the direction perpendicular to the loading axis. The mechanism of this “rafting” phenomenon is studied in terms of the movement, reactions and accumulation of dislocations in γ channels. Characteristics of the dislocations which accumulate on the γ-γ′ interfaces are discussed and the internal stresses generated by the accumulation of the glide dislocations are analyzed in terms of the geometrically necessary dislocations which accompany the gradient of the plastic shear strain.

Direct Observation of Field Emission Sites in a Single Multiwalled Carbon Nanotube by Lorenz Microscopy

Emission sites were observed as bright spots near the tip end of a multiwalled carbon nanotube (MWNT) by means of Lorenz microscopy. The bright spots appeared above electric fields as electrons were emitted. A marked fluctuation was observed in the emission current above 20–30 µA, which was closely related to structural changes at the tip of the MWNT. The layers of the MWNT were peeled off during field emission and they functioned as the second emission sites for the concentration of electric field.

In situ observation of field emissions from an individual carbon nanotube by Lorenz microscopy

In situ observation of field emissions from an individual carbon nanotube (CNT) was performed by Lorenz microscopy. A bright spot appeared by Lorenz microscopy at the end of the CNT tip during field emission. The bright spot is assumed to be related to the emission site on the CNT. A drastic fluctuation was observed in the emission current above a few tens of microamperes, which was closely related to structural changes at the tip of the CNT. The layers of the CNT were peeled off and they worked as a second emission site by concentration of the electric field.

Distinct Chemical Contrast in Adhesion Force Images of Hydrophobic–Hydrophilic Patterned Surfaces Using Multiwalled Carbon Nanotube Probe Tips

In this paper, we describe a fabrication procedure for large-diameter carbon nanotube probe tips (CNT tips) for atomic force microscopy, the tip-end chemistry of the CNT tips, and their advantage drawn from the study of adhesion force imaging in an ambient atmosphere on a patterned hydrophobic and hydrophilic self-assembled monolayer, which has been prepared by a microcontact printing method. Force titration measurements in phosphate buffer solutions reveal that the CNT tip has retained carboxyl groups at its end. In adhesion force imaging, a distinct chemical contrast is obtained for the patterned surfaces as compared to a case using a silicon nitride tip. The origin of the distinct contrast is discussed in terms of the tip-end chemistry featured by carboxyl groups and a possible weakening of capillary forces of water caused at around the tip–sample interface because of the intrinsically hydrophobic nature of CNTs.

In Situ Transmission Electron Microscope Observation of Carbon Nanotubes in Electric Fields

Transmission electron microscope is used to examine the movements of carbon nanotubes in electric fields. Carbon nanotubes lying along the surface of the cathode electrode start to move into alignment with the electric field vector when the field strength reaches 0.5 V/µm and become increasingly well-aligned with the vector as field strength increases. The carbon nanotubes return to their original positions when the electric field strength returns to zero. We also examine the abrupt breakdown of carbon nanotubes when the electric field is maintained at 5.5 V/µm. The corresponding breakdown emission current density is estimated as 3.4×107 A/cm2. The distance between the nearest nanotubes standing to align with the electric field vector is approximately 2 µm. This fact means that emission site density could be increased up to 3×107 points/cm2 (which corresponds to one tube for each 2 µm square).

New inline AFM metrology tool suited for LSI manufacturing at the 45-nm node and beyond

A new inline metrology tool utilizing atomic force microscope (AFM) suited for LSI manufacturing at the 45-nm node and beyond has been developed. The developed AFM is featuring both of high-speed wafer processing (throughput: 30 WPH) and high-precision measurement (static repeatability: 0.5nm in 3σ). Several types of carbon nanotube (CNT) probes specially designed for the AFM have also been developed. The combination of Advanced StepInTM mode and CNT probes realizes high precision measurement for high-aspect-ratio samples such as photoresist patterns. In Advanced StepInTM mode, a probe tip approaches and contacts a sample surface, and then moves away from the surface and toward a new measurement position. A series of these actions is performed in a short time (3.8 ms for single measurement point) full-automatically. Advanced StepInTM mode not only ensures gentle probe tip contact and precise measurement of high aspect ratio samples, but also minimum tip wear. CNT probes can provide long term performance, while eliminating the need for probe exchange. The developed AFM also realizes flatness measurement of 10-nm level in a wide area of 40x40-mm maximum. This performance is sufficient for the evaluation of CMP processes at the 45-nm node.

Three-dimensional evaluation of an independent multi-walled carbon nanotube probe by tomography with high-resolution transmission electron microscope

We evaluated an independent multi-walled carbon nanotube (MWNT) probe by using tomography with a high-resolution transmission electron microscope to verify the three-dimensional structure of the probe tip. The new method of probe evaluation revealed the following features: (i) cutting the end of the MWNT probe caused the wall structure to disintegrate and encapsulated the graphene sheets fragmented by the discharged pulse; (ii) the cap of the MWNT probe was an open cylinder covered by walls similar in shape to a rectangular slit; (iii) the grooves of the inner walls of the MWNT probe, which were created by the discharge cutting method, maintained a cylindrical shape that was different from the peeling-off mechanism.

Electrode material dependence of two-dimensional electron and vapour density distribution over vacuum arc discharge

Electrode material dependence of intense-mode vacuum arc behaviour was systematically investigated by using the Shack-Hartmann method capable of simultaneously visualising two-dimensional electron and metal vapour density distributions from single-shot recordings. The electrode materials studied included Cu, CuCr (Cu75Cr25 wt. %), WC, and AgWC (Ag40WC60 wt. %). A comparison between the Cu and CuCr electrodes showed that the metal vapour densities for the CuCr decreased in an even shorter time scale than for the Cu. In the case of the WC electrodes, the widths of the electron density distributions became narrower as the arc current decreased although the electron densities hardly decreased in the decaying process of the arc current. The density measurements conducted at the late stage of the vacuum arcs demonstrated that the metal vapour densities around the anode were maintained at the highest value for the AgWC among the electrode materials in this study.